Skin patch including a temperature sensor

ABSTRACT

A skin patch includes first and second layers of material and a telesensor sandwiched between the first and second layers. The first layer has a coating of skin-compatible adhesive material on its face that is remote from the second layer.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit of Provisional Application No.60/267,593 filed Feb. 8, 2001. The entire disclosure of ProvisionalApplication No. 60/267,593 is hereby incorporated by reference hereinfor all purposes.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a skin patch including a telesensor,and particularly to a skin patch that includes a temperature sensor.

[0003] As used herein, the term “telesensor” means a device that allowsa physiological parameter to be monitored at a distance and “temperaturesensor” means a telesensor for which the physiological quantity is bodytemperature. A temperature sensor includes an element whose behaviordepends substantially on temperature of the element and that emits asignal from which the temperature of the element can be derived.

[0004] Skin patches have been proposed for several purposes. One type ofskin patch has been used to collect small quantities of perspiration inan absorbent pad. After the monitoring period, the patch can be removedfrom the subject's skin and the perspiration recovered from theabsorbent pad. Through analysis of the perspiration, the presence andamount of various chemical species can be determined. For example, U.S.Pat. No. 4,329,999 (Philips) describes a skin patch useful for drug oralcohol detection. Skin patches have also been proposed in whichchemically active strips are employed instead of absorbent pads. Thestrips react to specific chemicals of interest. For example, U.S. Pat.No. 4,444,193 (Fogt et al) discloses a skin patch in which twoconcentric circular reaction areas of chemically treated absorbent paperreactive to chloride in the perspiration are used for indicating cysticfibrosis. U.S. Pat. No. 4,732,153 (Philips) discloses a skin patchcontaining an active medium such as charcoal, which traps theperspiration and retains it during the monitoring period. Aftermonitoring, the active medium is recovered and analyzed for the presenceand amount of the chemical of interest. Skin patches having multipletest zones containing different respective active media, for collectionand detection of different chemical species, have also been proposed.

[0005] Skin patches for administering chemicals transdermally have alsobeen proposed. Skin patches have been developed to administermedications for pain relief and for hormonal and other replacementtherapies.

SUMMARY OF THE INVENTION

[0006] In accordance with the invention there is provided A skin patchcomprising a first layer of material, the first layer having first andsecond opposite main faces and the first main face having a coating ofskin-compatible adhesive material, a second layer of material, thesecond layer having first and second opposite main faces and the firstmain face of the second layer being in confronting relationship with thesecond main face of the first layer, and a telesensor for emitting asignal that represents a physiological parameter sensed by thetelesensor, the telesensor being sandwiched between the first and secondlayers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a better understanding of the invention, and to show how thesame may be carried into effect, reference will now be made, by way ofexample, to the accompanying drawings, in which

[0008]FIG. 1 is a top plan view of a first skin patch in accordance withthe present invention; the telesensor is a temperature sensor and FIG. 1shows the patch with the cover layer removed and illustrates the layoutof the components of the temperature sensor,

[0009]FIG. 2 is a schematic sectional view of the skin patch that isshown in FIG. 1,

[0010]FIG. 3 is a schematic block diagram of the temperature sensorincluded in the skin patch shown in FIG. 1, and

[0011]FIG. 4 is a schematic sectional view of a second skin patch inaccordance with the present invention.

DETAILED DESCRIPTION

[0012] The skin patch shown in FIGS. 1-3 includes two integrated circuitchips 2, 4, two button cell batteries 6 connected to power supplyterminals of the chip 2, and an antenna 8 connected to an outputterminal of the chip 2. The integrated circuit chip 4 is connected to athermistor 12 (FIG. 3) and several passive components (not shown). Theelectrical resistance of the thermistor 12 depends substantially on itstemperature

[0013] The button cells 6 are small and of relatively low profile andare of the type that are commonly used for hearing aids. The integratedcircuit chips 2, 4 and associated components, the button cell batteries6 and the antenna 8 form a temperature sensor. The temperature sensor,when active, periodically measures the temperature of the thermistor andthen transmits the measurement information via an RF link. A receivingunit receives the transmission and derives the temperature.

[0014] The chips 2, 4, the batteries 6 and the antenna 8 are attached toan electrically insulating flexible circuit substrate 14, as are allother electrical components of the sensor. The flexible circuitsubstrate is provided on its undersurface with a coating 16 of anadhesive material. A removable protective layer 20 of paper adheres tothe adhesive coating 16. The skin patch further includes a top or outerprotective layer 22 of thermally insulating material over thetemperature sensor and adhesively bonded to a peripheral margin of theflexible circuit substrate 14.

[0015] In use of the skin patch, the paper layer 20 is removed to exposethe adhesive coating 16 and the patch is applied to the skin of asubject. The thermistor temperature equilibrates with skin temperatureof the subject. The temperature sensor, if active, measures thetemperature of the thermistor and transmits the temperature information.

[0016] In order for the skin patch to be physiologically compatible withthe subject, the material of the adhesive coating should be one that canremain in contact with the skin for an extended period of time, e.g.four to five days, without causing an unacceptable reaction.

[0017] For a normal activity level, moisture transpires through the skinof a human subject at a moisture vapor transmission rate (MVTR) of about425 g/m² per 24 hours. Vigorous exercise produces a higher MVTR whilemore sedentary behavior results in a lower MVTR. Moisture thattranspires through the skin of a human subject may adversely affect theelectrical components of the skin patch, i.e. the integrated circuitchips, the cells and the antenna, and accordingly it is desirable toprotect these components from exposure to such moisture. The flexiblecircuit substrate generally has a very low MVTR capacity, so that if theflexible circuit substrate were imperforate, moisture would not permeatethrough the substrate and affect the electrical components. However, itis not desirable that moisture should be trapped in contact with theskin and therefore the skin patch must provide at least sufficient MVTRcapacity for normal activity. This requirement necessitates that eachlayer of the skin patch have an MVTR capacity of at least 425 g/m² per24 hours. Moreover, the upper layer must in addition be resistant toliquid water exposure. A number of commercially available materials havesufficient MVTR capacity and are resistant to liquid water.

[0018] Referring to FIG. 1, the patch is sufficiently large, and theelectrical components are sufficiently small, that a substantialproportion of the area of the flexible circuit substrate 14 is notoccupied by the electrical components. Several holes 24 through thesubstrate allow moisture to pass through the substrate. The holes 24 maybe spaced away from the more sensitive electrical components.

[0019] Moisture that passes through the holes 22 in the substrate andenters the upper layer 22 will tend to permeate the entire upper layer.A conformal coating 28 of a polyurethane or epoxy material is providedover the electrical components in order to protect them from corrosionand humidity effects due to moisture present in the upper layer.

[0020] Referring to FIG. 3, the integrated circuit chip 4 implements atimer 32, and the timer 32, the thermistor 12 and passive componentsimplement an astable multivibrator 30. The astable multivibrator 30generates a periodic output signal in the form of a square wave having aduty cycle that depends on the resistance of the thermistor 12. Theoutput signal of the multivibrator 30 is supplied to a microcontroller34 implemented in the integrated circuit chip 2. The microcontrollerincludes a counter 36, which uses a clock signal generated by anoscillator 38 to measure the length of time in each cycle of the outputsignal of the multivibrator for which the output signal is in the logichigh state and the length of time for which the output signal is in thelogic low state, and calculates the ratio of these times. Since the dutycycle of the output signal depends on the temperature of the thermistor12, this ratio also depends on the temperature of the thermistor. Theratio is encoded by an encoder 40 as a component of a digitaltransmission packet. The encoder supplies the digital transmissionpacket to a radio transmitter 42 which is also implemented in the chip 2and uses the transmission packet to modulate a carrier and the modulatedcarrier drives the antenna 8 for radiating the signal.

[0021] The skin patch is used in conjunction with a receiving unit (notshown) which includes an antenna for receiving the signal radiated bythe transmitting antenna 8, an amplifier for amplifying the receivedsignal, a microcontroller for decoding the received signal andrecovering the ratio value and calculating temperature based on theratio value, a memory for storing calculated temperature values, and areadout device for displaying the calculated temperature values.

[0022] In order to prolong shelf life and operating life of the skinpatch, the microcontroller controls supply of power to the multivibrator30 and the transmitter 42. The microcontroller 34 further controls itsown power consumption by use of low-power sleep and suspend modes.

[0023] The microcontroller 34 is initially activated to its normalactive mode by applying a specific signal sequence to contact pads 54,which are exposed on the paper layer and are connected to themicrocontroller through vias that pass through the flexible circuitsubstrate and the paper layer 20. In the normal mode, the multivibratorand transmitter are powered. When the microcontroller has beenactivated, it periodically returns to and exits from the suspend mode.In the suspend mode of the microcontroller, the multivibrator andtransmitter are not powered.

[0024] When the skin patch is first assembled, the microcontrollerenters a calibration mode and then enters the low-power sleep mode. Inthe sleep mode, the multivibrator and the transmitter are not powered.From this time until the skin patch is activated, the only powerconsumed is that which is required to maintain the microcontroller inthe sleep mode. When the device is to be put to use, an activatorcircuit, which may be incorporated in the receiving unit, applies thewake-up signal sequence to the contact pads 54. If the proper wake-upsignal sequence is detected by the microcontroller, the microcontrollerenters the normal operating mode, in which it supplies operating currentto the multivibrator and the transmitter for measuring temperature andtransmitting temperature information. The active mode alternates withthe stand-by mode to conserve power when not measuring or transmitting.

[0025] When the microcontroller detects the proper wake-up signalsequence, it also powers the multivibrator and the transmitter in orderto measure the temperature, as sensed by the thermistor, and send ashort repeated sequence of measurement data, which includes a uniqueidentifier for the temperature sensor. This data, transmitted using theantenna 8, is interpreted by the receiving unit, which provides the userwith an indicator that successful activation has been achieved. The usercan then disconnect the skin patch from the activation circuit. Thepaper layer is then removed, thereby also removing the contact pads 54and effectively rendering the activation terminals of themicrocontroller inaccessible. The patch is ready to be applied to thesubject's skin.

[0026] After transmitting the measurement and identification data, themicrocontroller removes power from the multivibrator and transmitter 42and enters the standby mode. While in this standby mode, a timer 58 inthe microcontroller continues timekeeping functions and after apredetermined interval wakes the microcontroller into active mode. Themicrocontroller activates the circuits when appropriate and performs theoperations described above in connection with measuring the ratio andtransmitting the encoded data. The microcontroller then removes power,re-enters the standby mode, and repeats the cycle.

[0027] Further details regarding the operation of the temperature sensorare disclosed in copending patent application Ser. No. 10/017,098 filedDec. 12, 2001, the entire disclosure of which is hereby incorporated byreference herein for all purposes.

[0028]FIG. 4 illustrates a modification of the skin patch described withreference to FIGS. 1-3. In accordance with FIG. 4, the coating ofphysiologically compatible adhesive material is not provided on theundersurface of the flexible circuit substrate. The skin patch includesan additional layer 60 adhesively bonded to the undersurface of theflexible circuit substrate 14 and the adhesive coating 16 is provided onthe undersurface of the layer 60. The layer 60 is made of a materialhaving an MVTR capacity of at least 425 g/m² per 24 hours.

[0029] It will be appreciated that the invention is not restricted tothe particular embodiment that has been described, and that variationsmay be made therein without departing from the scope of the invention asdefined in the appended claims and equivalents thereof. For example, inone alternative embodiment the microcontroller may be activated bytransmitting the wake-up signal sequence from the activation unitoptically instead of electrically. Further, it would be possible toprovide sufficient memory in the temperature sensor to recordtemperature measurements over several days, in which case the storeddata could be retrieved after the measurement period and it might not benecessary to include a transmitter and an antenna in the temperaturesensor. Although the invention has been described with reference to atemperature sensor, the invention is also applicable to othertelesensors, for example telesensors that emit signals representative ofheart rate, heart rate interbeat interval, activity level, includingactivity level at the sensor location, and blood oxygen level. Unlessthe context indicates otherwise, a reference in a claim to the number ofinstances of an element, be it a reference to one instance or more thanone instance, requires at least the stated number of instances of theelement but is not intended to exclude from the scope of the claim astructure or method having more instances of that element than stated.

1-13. (canceled)
 14. A device for acquiring physiological datacomprising: a support layer having first and second opposite main facesand the first main face having a coating of skin-compatible adhesivematerial, a sensor element for sensing a physiological parameter andgenerating a signal representative of the physiological parameter, thesensor element being attached to the support layer at the second mainface thereof, a data storage element for measuring the signal generatedby the sensor element and storing values representing the signalmeasurements, and an output means for retrieving the stored values. 15.A device according to claim 14, wherein the signal generated by thesensor element represents evolution of the physiological parameter as afunction of time during a measurement period and the data storageelement measures the signal generated by the sensor element during ameasurement period.
 16. A device according to claim 14, wherein thesignal generated by the sensor element represents evolution oftemperature as a function of time during a measurement period and thedata storage element measures the signal generated by the sensor elementduring a measurement period.
 17. A device according to claim 14, whereinthe support layer is a flexible circuit substrate of electricallyinsulating material.
 18. A device according to claim 17, wherein theflexible circuit substrate is formed with through holes spaced from thesensor element.
 19. A device according to claim 18, wherein the sensorelement includes at least one electrical component attached to theflexible substrate, and the holes are spaced from said electricalcomponent.
 20. A device according to claim 14, wherein the physiologicalparameter is temperature and the signal generated by the sensor elementis a temperature signal.
 21. A device according to claim 20, wherein thesensor element includes an astable multivibrator incorporating athermistor, the astable multivibrator generating a square wave outputsignal having a duty cycle that depends on the temperature of thethermistor, and the temperature sensor further comprises amicrocontroller that receives the output signal of the multivibrator andgenerates said temperature signal.
 22. A device according to claim 14,wherein the support layer comprises an attachment layer having first andsecond opposite main faces, the first main face of the attachment layerbeing the first main face of the support layer, and a flexible circuitsubstrate having first and second opposite main faces, the first mainface of the flexible circuit substrate being in confronting relationshipwith the second main face of said attachment layer and the second mainface of the flexible circuit substrate being the second main face of thesupport layer.
 23. A device according to claim 14, further comprising asecond layer having first and second main faces, wherein the first mainface of the second layer is in confronting relationship with the secondmain face of the support layer and the sensor element is between thesupport layer and the second layer.
 24. A device according to claim 23,wherein the second layer is a conformal coating over the sensor element.25. A device according to claim 23, wherein the second layer is made ofa material that is permeable to water vapor at its first face and isimpermeable to liquid water at its second face.
 26. A device accordingto claim 25, further comprising a conformal coating of electricallyinsulating and water impermeable material over the sensor element.
 27. Adevice according to claim 23, wherein the sensor element is atemperature sensor and the second layer is made of a thermallyinsulating material.
 28. A device according to claim 23, wherein thesupport layer is made of a material that is permeable to water vaporpresent at its first face and the second layer is made of a materialthat is permeable to water vapor at its first face and is impermeable toliquid water at its second face.
 29. A device according to claim 14,wherein the support layer is permeable to water vapor present at itsfirst main face.